The problem of effective utilization of computer resources, such as a data storage file system in a multi-user environment, has existed from virtually the first use of computers. In such data storage file systems, the data storage files are traditionally separated into several classes: the personal files of the user, the data storage files shared by all the users, temporary files, etc. The classes of these data storage files usually differ in their disposition in the data storage file system and in their access mode. Depending on the settings of the operating system, only the owner of the data storage file or someone with explicitly declared access rights has write-ability access to these data storage files. Everyone has write-ability access to temporary data storage files. The majority of users have read-only access to the general system files. In the system area, only the auxiliary data storage files are deposited. Therefore, the auxiliary data storage file provides the working information for the operating system.
Ordinary computer users generally are not interested in modifications of the content of system data storage files. Therefore, most often, all of the system data storage files, including the configuration of files, are usually seen by all the users of the operating system, and they are typically seen only in the read-only mode. Nevertheless, it is often necessary to provide for the possibility of multiple users making corrections to the system area. For example, for the configuration of system utilities, it is desirable that the unique data storage file modifications made by each computer user do not influence the configurations of others. This means that each computer user should be provided with an independent file system tree with the data storage files suitable for writing. If there are many such computer users with independent file systems on the same computer, it would be essential to implement an effective method for each computer user to access such data storage files. Traditionally, this problem is solved in two ways: 1) copying corresponding data storage files for each computer user; 2) using the data storage file system to create and support hard links. With these solutions, multiple references would need to be created to the same data storage file using different names.
Copying corresponding data storage files for each computer user leads to the multiple duplication of data storage files and is not an efficient use of data storage resources because of the typically large size of the system area. Another possible solution to this problem in the form of using the file system to create and support hard links, limits the user's ability to modify the data storage file system.
Since all of the users view the same system data storage file, its modification by one computer user will be immediately apparent to the other computer users who have access to the hard links of the same data storage file.
Thus, the need arises for an efficient solution that will allow many computer users to work on one physical computer. Each of the computer users has his/her own version, not only of their personal local data storage files, but also the system file area of the operating system.
Other prior art solutions have been discussed in the following references (See Bibliography). Partial solutions for this problem exist in many operating systems. For instance, in a UNIX type operating system, the primitive chroot is used to provide a certain level of security and separation for the computer users to allow them to have their own version of root data (Bach 1987, THE DESIGN AND IMPLEMENTATION OF THE 4.4BSD OPERATING SYSTEM). But this solution assumes that each computer user should have his/her own unique data storage file system tree and that the data storage file system tree cannot be effectively implemented.
Another partial solution is the separation of read and write operations provided by a so-called Union file system (Pendry 1995, THE DESIGN AND IMPLEMENTATION OF THE 4.4BSD OPERATING SYSTEM). The Union file system proposes a mount of one data storage file system tree on top of another tree. In such a case both trees become visible during the namespace lookup procedure. This allows the creation of separate write and read areas, but does not allow modification of data storage files which reside in the read-only area.